1. Technical Field
The present invention relates to an actuator device including a piezoelectric element formed of a lower electrode, a piezoelectric layer, and an upper electrode, and displaceably provided on a substrate with a zirconium oxide layer interposed therebetween, the substrate having a silicon oxide layer formed by thermal oxidation on at least a surface thereof, a method of manufacturing the same, and a liquid-jet head including the actuator device as a liquid-jet unit.
2. Related Art
As a piezoelectric element used in an actuator device, there is an element formed by sandwiching a piezoelectric layer made of a piezoelectric material exhibiting an electromechanical conversion function, for example, a crystallized dielectric material, between two electrodes of a lower electrode and an upper electrode. Such an actuator device is generally called a flexure-vibration-mode actuator device and is mounted on and used in a liquid-jet head, for example. Here, a typical example of the liquid-jet head includes an ink-jet recording head, for example, in which a part of a pressure generating chamber communicated with a nozzle orifice for ejecting ink droplets is formed of a vibration plate, and ink droplets are ejected from the nozzle orifice by displacing this vibration plate with a piezoelectric element so as to pressurize the ink in the pressure generating chamber. Meanwhile, as the actuator device to be mounted on the ink-jet recording head, for example, there is a device in which a piezoelectric material layer is formed over the entire surface of the vibration plate by a film-forming technique and this piezoelectric material layer is cut into shapes each corresponding to the pressure generating chamber by a lithography method to form piezoelectric elements provided independent from one another for the respective pressure generating chambers.
As such a piezoelectric element, there is an element formed of a lower electrode, a piezoelectric layer, and an upper electrode, and displaceably provided on a substrate with a zirconium oxide layer interposed therebetween, the substrate having a silicon oxide layer formed by thermal oxidation on a surface thereof (as disclosed in JP-A-2003-110158, JP-A-2005-166719, and JP-A-2005-295786, for example).
Formation of the silicon oxide layer on the surface of the substrate by thermal oxidation prevents pin holes and the like as compared to the case of forming the silicon oxide layer by use of a vapor deposition method such as a CVD method. Moreover, this leads to the formation of a layer formed on the silicon oxide layer which has no pin holes, the layer not being affected by the pin holes, thus eventually obtaining a desired actuator device. Meanwhile, in the liquid-jet head, passages such as the pressure generating chambers are formed by wet-etching the substrate. Here, a silicon oxide layer which has no pin holes is also needed in order to cause the silicon oxide layer to function as an etching stop layer at the time of the wet etching. Accordingly, the silicon oxide layer without pin holes has been obtained by forming the silicon oxide layer by thermal oxidation. Meanwhile, a component constituting the piezoelectric layer is diffused from the piezoelectric layer toward the silicon oxide layer at the time of baking at a high temperature a “precursor film” which is a state of the piezoelectric layer before crystallization. Here, the component diffused from the piezoelectric layer is prevented by the zirconium oxide layer.
However, when the zirconium oxide layer is formed on the silicon oxide layer formed by the above-described thermal oxidation, although there is no effect by the pin holes as very few pin holes exist on the silicon oxide layer, there has been a problem that the zirconium oxide layer having a uniform thickness cannot be formed because part of crystals constituting the zirconium oxide layer have grown abnormally due to a different reason from the effects by the pin holes, whose detailed cause of generation is unknown. As a result, there has been a problem that an actuator device having a desired displacement characteristic cannot be obtained since concave-convex portions formed on the zirconium oxide layer are transmitted to the lower electrode, the piezoelectric layer, and the upper electrode formed on the zirconium oxide layer, and thereby negatively affecting the state of film formation thereof.